Answer
C
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A killed vaccine (or inactivated vaccine) is a vaccine consisting of bacteria, virus particles or other pathogens that have been killed to reduce virulence and thus prevent infection from the vaccine. They can be killed by chemicals or heat. The pathogens of inactivated vaccine produce a weaker immunological response, so multiple "booster" injections and immunologic adjuvants are given to provide effective immunity against the inactivated pathogen. The purpose of adjuvant is to increase the antigen-specific immune response.
